Up to now, there have been widely used a large variety of information equipments that are provided with a pickup unit using a photoelectric conversion device such as a C-MOS (Complementary Metal Oxide Semiconductor) or a CCD (Charge Coupled Device) as an image pickup device that converts light coming from a pickup lens to electronic signals to output thus generated electronic signals.
Among those information equipments, portable small-sized information equipments, which are intended for mobile use, are desired to make their pickup lens and image pickup device smaller with high pickup performance of their pickup unit maintained and to have an optical zoom in view of their purpose of use. For example, a digital camera and a portable radiotelephone equipment or a cellular phone having a camera built therein are required to have a pickup lens provided with optical zoom function. Moreover, such a pickup lens is required to reduce the length on the optical axis from a lens surface closest to a subject to be shot to the light-receiving surface of an image pickup device, that is, the entire length of a pickup lens. Furthermore, miniaturization of an image pickup device as well as high resolution are required.
Since optical power or optical magnification of above-described pickup lens provided with optical zoom function is variable, one lens group among plural lens groups is moved along the optical axis. For example, as for a pickup lens of triple lens group configuration, when varying optical power, the second lens group on the optical path works as a power-varying lens or a lens to vary optical power, and is moved along the optical axis.
As a pickup lens provided with optical zoom function for use in above-described information equipments, there is disclosed a pickup lens of triple lens group configuration provided with optical zoom function that has lens groups having power in the order of negative, positive, positive on the optical path from a subject to be shot in Japanese Laying-Open Patent 2002-55278.
Furthermore, as a pickup lens for use in above-described information equipments, there is disclosed a pickup lens of quadruple lens group configuration provided with optical zoom function that has lens groups having power in the order of negative, positive, positive, positive on the optical path from a subject to be shot in Japanese Laying-Open Patent 2002-72095.
As for the pickup lens disclosed in Japanese Laying-Open Patent 2002-55278, the entire length is too long when built in an information equipment, and the first lens group is moved when varying optical power, which leads to complicated mechanical design and difficulty in realizing low cost. In such a pickup lens, since a lens group closest to a subject to be shot is moved, a lens frame has to be drawn out from the main equipment body for zooming, there is a fear that an information equipment may be broken due to drop impact or contact with other objects.
On the other hand, even if the pickup lens disclosed in Japanese Laying-Open Patent 2002-72095 is desirable in crashworthiness from a point of view that a lens group closest to a subject to be shot is fixed when varying optical power, since the last lens group is positive, it is difficult to reduce the back focal distance, which leads to difficulty in miniaturizing an information equipment.